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Old 12-05-2016, 05:09 AM
sn1987 sn1987 is offline
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Restraint for structure dimensioning

Hello to everybody.
I have a question for you.
I have to design a second deck above the main deck of a small passenger boat with this main particulars:

- LOA 17.50 m
- B 4.5 m
- D 1 m
max passenger 60


For this deck I think to create a structure with steel vertical supports and wooden beams and shell(see the screenshot). The joint between supports and beam is realised by bolts (see the screenshot). For dimensioning I use Multiframe software.

My doubts are about the choose of the node's restraints that I have to use for correctly dimensioning the structure.
Could anyone help me?
Thanks
Attached Thumbnails
Restraint for structure dimensioning-cattura.jpg  Restraint for structure dimensioning-1.jpg  
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  #2  
Old 12-05-2016, 05:33 AM
Ad Hoc Ad Hoc is offline
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Your question is too vague.

As an engineer, you need to be more succinct - less ambiguity!
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Old 12-05-2016, 06:30 AM
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gonzo gonzo is offline
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You should design this structure as part of the whole ship. For example, if the hull flexes or twists, it will deform the upper deck and make the fasteners fail.
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Old 12-05-2016, 07:11 AM
sn1987 sn1987 is offline
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Thanks for the answers.
Probably I made the question in a wrong way.
1) Firstly I have to study the local stress of the new deck.
The joint I would to realize is like in the screenshot, so that I need is understand the correct restraints that I have to assign to the bolts to obtain a realistic results indipendently the applied loads (nodes n16,18,21,24 on the screenshot 1 )
2) Secondly I have to study the global stress of the whole structure as gonzo said.
Attached Thumbnails
Restraint for structure dimensioning-2.jpg  Restraint for structure dimensioning-3.jpg  Restraint for structure dimensioning-1.jpg  

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Old 12-05-2016, 07:46 AM
TANSL TANSL is offline
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The first thing I advise you is that you do not use two different materials in the same structure. The second is that, if possible, flee from bolted or riveted joints. The more holes you make in the wooden beams, the more problems you will have, structural, rotten wood due to humidity, etc ...
Select a Classification Society for your boat and let yourself be guided by its rules, advice and formulas.
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Old 12-05-2016, 09:35 AM
sn1987 sn1987 is offline
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I thought to use two different materials because the boat is wooden built and I have to leave the both sides open as in the picture. So I thought the steel vertical supports are a good solution. Anyway as TANSL said this way could have various problems due to different nature of used materials.
I'm a fresh graduated and so I haven't a lot of experience, then any idea and suggestion is very important for me. What would you do in my case for scantling the structure?
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Old 12-05-2016, 09:55 AM
TANSL TANSL is offline
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The wood works very well to compression, so you could use that material for pillars.
Each cross section should form a closed ring and probably in the union of the horizontal sections with the vertical ones you should place consoles that form the embedment that the beams need at their ends.
With complete a GA would be possible study the most appropriate structure and give you more concrete and appropriate advice.
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Old 12-05-2016, 10:48 AM
sn1987 sn1987 is offline
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I attached the profile, front and upper deck plan. In these screenshot are also printed the two stairs that can be used as support to upper deck. If it is helpful I can post the 3dm file.
Attached Thumbnails
Restraint for structure dimensioning-render.jpg  
Attached Files
File Type: pdf deck1.pdf (108.4 KB, 22 views)
File Type: pdf front.pdf (111.1 KB, 21 views)
File Type: pdf longitudinal.pdf (43.7 KB, 22 views)
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  #9  
Old 12-05-2016, 11:24 AM
TANSL TANSL is offline
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The structure of that deck seems to float in the air. Since this is not possible, it is necessary to place sufficient supports. Naturally it depends on the weight that you want to carry on the deck, but the normal thing, in order not to have huge beams and long.girders would be to place supports at the ends of each beam and intermediate supports that support the girders.
Before moving on to 3D rendering, you should do some schematics, even by hand and with pencil, on what your structure, how main and secondary elements will look like and how they can lean on each other. The bottom, the side, the reinforcements of the bottom, the reinforcements of the side, the beams and girders of the lower deck, etc ... and the elements of support of the high deck, .... everything must form a properly connected assembly .
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Old 12-05-2016, 04:24 PM
Ad Hoc Ad Hoc is offline
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Quote:
Originally Posted by sn1987 View Post
The joint I would to realize is like in the screenshot, so that I need is understand the correct restraints that I have to assign to the bolts to obtain a realistic results indipendently the applied loads (nodes n16,18,21,24 on the screenshot 1 )
The restraint, in your FE program would be "Built-in". From the results, you need to obtain the bending moment at each connection (node) as well as the shear force. From these values, you can design the bolted connect to safely satisfy the applied loads.

However, there is no need for any FE calculation, as this type of analysis is very simple and straight by hand.
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Old 12-05-2016, 11:51 PM
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PAR PAR is offline
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I don't understand the issues here. The calculations aren't particularly difficult and the structure itself doesn't appear to present any major concerns, assuming the yacht is capable of tolerating this dramatic increase in its CG, with a worst case scenario crowd on that new deck. I also agree with John in that a mechanical connection is certainly viable and even dissimilar materials, such as alloy supports for the wooden deck frame. In fact, this is how I would approuch the problem, if only to save some weight and physical volume.

The drawings so far provided, are little more than pretty pictures and haven't any of the usual attributes, seen in a construction plan. Try skipping the shadows, 3D bird's eye views, colors and stuff and focus on the problems, such as an appropriate way to connect the beams to the perimeter carlin, preferably such as to not promote moisture ingress or entrapment or having the appropriate scantlings for the anticipated loading, given the worst case scenario possability and safety margins (etc.). Work with a simple orthographic projection and pretty it up (if necessary), once you've refined the details. Frankly, I've never sold a set of plans, because of a pretty 3D image. These are for advertising brochures and only distract from the necessary detail, typically found in a technical drawing.
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Old 12-06-2016, 12:13 AM
JSL JSL is offline
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If a passenger boat you will probably have to meet regulatory requirements and these will govern the material, design & construction
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Old 12-06-2016, 03:57 AM
sn1987 sn1987 is offline
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Probably I made a bad impression.
Anyway:
1) My intention wasn't to publicate any kind of technical drawing. I posted the rendered screenshots only for clarify and better illustrate the problem. So I knowthey are incomplete and inadequate to rapresent the phisical phenom.
3)My original question was to know the correct type of restraints to use (fixed, pinned, horizzontal roller, vertical roller) for example in the joint wood-steel that I had hypothesized.
4) I would only know how professionists more expert than me would approach this problem and what kind of solution they would use.
5) In the actual condition the boat has got GMt=2.5 m

Thanks to all
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Old 12-06-2016, 09:28 PM
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gonzo gonzo is offline
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You would not use any kind of roller constraints. This is basically a rigid structure, at least for an initial analysis. The vertical support are slender columns pinned at both ends. However, you should first consider what kind of loads and in which directions they will act before starting to design a structure.
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Old 12-07-2016, 01:10 AM
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sn1987

Forget the hull flexing for the moment as it is the least of your concern. At 17 meters, hulls are rigid and does not require global strength analysis.

In your first post, you showed main transverse beam supported at each end with a secondary transverse beam interspaced. In later post, you showed multiple beams with interspacing of about 5 or 6.

What is lacking in the illustration is the proper diagram to analyze it accurately. Here are the basic rule.

1. The main transverse beams are fixed on both ends. Primary structures are always reinforced at the end connections with a bracket, a beam knee, or a hanging bracket. If the primaries deflects more than the limiting factor, it must be supported by pillars located in between the support points.

2.The secondary transverse beams support the plate to reduce panel size. Because it is of a smaller size, it is supported at the ends by a girder which is not shown in your diagram. It is smaller than the primary, it must be supported by at least one primary Longitudinal to prevent too much flexing. The primary longitudinal is supported at the ends by the primary transverse/beam. Smaller longitudinal stiffeners are needed to reduce panel size.

3. The girder supports the transverses and in turn is supported by vertical posts. The girder strength is dictated by the distance between two primary transverses.
To sum up, the flooring plate is supported by the secondary beams and longitudinals. the primaries and secondary is supported by the girders, the girder is supported by the vertical columns.

Now for the load analysis:
1. The load is uniformly loaded when the paxs are sitting in their assigned seats. During disembarkation, the paxs move to the center isles to queue. This is a concentrated load. The greatest shear is at the edge of the fixed support points, uniformly loaded. This distance moves away if the ends are bracketed. Check for shear perpendicular to the grain. For stress in the outer fibers, check both for tension and compression as it reverses directions during the different load analysis. Wood has different mechanical properties for tension/compression. Compression on the top end (center) during concentrated load and tension reaction (at fixed ends) during the uniformly distributed load. Check deflection limitation.

2. At the fixed end, check for vertical shear at the edge of the support or if bracketed (highly recommended) at the end of the bracket.

3. The bolted joint must be in compression, hence a fixed plated and a large washer and nut on the other side. If more than one bolt is used, a non fixed plate can be used. Do not use fixed plate both sides. Check bolt shear requirement.

3a. The spacing of the vertical post is dictated by the spacing of the girder. The girder must be able to handle the load.

4. In the deflection analysis, the beam will act as a fulcrum or a lever on the bolt at a distance away from the edge of the support point. Check for the wood's vertical shear. A vertical shear is always accompanied by a horizontal shear. Check the wood's horizontal shear properties. The along the grain and thru the grain shear properties of wood are different.

5. Add safety factor and the factor needed for the moisture content of the wood during operations. This data is available in Simplified Structural Design. In fact the design procedure is outlined in the book, much like designing a house with floors, beams, girders, and columns.

5a. Forget about the different CTE of wood and metal as the whole thing flexes and wood in the bolted joint will not be subjected to extreme temperature variations as in rocket science. If you adhere to the safe shear properties of the wood in the along the grain and vertical to the grain, you are in safe ground.

6. Lastly, check for the global modulus of the hull for flexing but this is entirely another topic.
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